The present invention relates generally to brake boosters, and more particularly relates to a multi-purpose sensor for a brake booster.
Most modern vehicles employ power brakes utilizing a brake booster. The brake booster uses a vacuum to multiply the force that a driver applies to the brake pedal. Briefly, the engine intake manifold provides a vacuum source to suck air out of the booster, producing a partial vacuum. Alternately, a separate vacuum pump can be utilized for this function. At least one diaphragm is positioned within the booster to define first and second chambers. When the brake pedal is undepressed, both the first and second chambers are at the low pressure of the partial vacuum.
When the brake pedal is depressed, a valve is opened allowing atmospheric air to enter the booster on one side of the diaphragm. This increases the pressure on that side of the diaphragm, say the second chamber for example, which assists in pushing the output rod, and in turn the piston in the master cylinder of the braking system. When the brake pedal is released, the valve seals off the outside air supply while reopening the vacuum to the second chamber. With the partial vacuum restored in both the first and second chambers, pressure on the diaphragm is equal and the system returns to its original position.
A number of different sensors and switches are utilized within the braking system and the brake booster which serve many different purposes. For example, within the braking system a pressure sensor is typically employed to detect the pressure of the braking fluid at the master cylinder. Among other things, the pressure sensor can detect when the driver applies the brakes while in a brake assist mode, i.e. when the electronic stability program utilizes the solenoid to apply force to the output rod and pressurize the master cylinder. Additionally, a brake light switch is typically employed for detecting when the brake is applied and causing the vehicle brake lights to be energized.
Within the booster, a displacement transducer, commonly referred to as a xcex94S sensor is utilized to detect the position of a first force transmitting member operatively connected to the brake pedal, relative to a second force transmitting member operatively connected to the diaphragm of the booster. Among other things, the xcex94S sensor can detect a failed boost situation, i.e. where the second chamber does not readily fill with atmospheric air to move the second force transmitting member forward into alignment with the first member. Further, a micro switch is typically used to determine whether or not the driver is pushing on the brake pedal. A travel sensor is typically employed to determine the position and rate of movement of the diaphragm relative to the outer casing of the booster. Accordingly, the travel sensor can detect whether the booster is active or not, and is primarily used to detect a panic brake situation. A panic brake situation occurs when the driver suddenly and quickly applies the brakes, which can be detected by the position and rate of movement of the diaphragm.
Unfortunately, while all of these sensors are important, they can be rather expensive and increase the overall cost of the braking system and the vehicle. Further, installation of these sensors can sometimes be difficult, and may require additional work or testing to ensure their operability. For example, brake lights switches are typically installed at the original equipment manufacturer""s assembly plant, and in some cases requires manual adjustments for proper performance. Accordingly, there exists a need for a simple, easy to install, and low cost alternative to the numerous and complex sensors currently used on braking systems and brake boosters.
The present invention provides a single sensor which can replace many if not all of the sensors noted above. The information retrieved from the sensor may also be employed in other applications. The sensor is preferably a capacitance-type sensor that detects the location and force applied to the sensor. In one embodiment, the sensor is integrally formed within a reaction disc in the brake booster. The reaction disc is coupled to the output rod which is linked to the master cylinder. The reaction disc receives forces from the brake pedal via a valve piston assembly, and also receives forces from a transfer member connected to the diaphragm of the brake booster.
Another embodiment includes forming the sensor within the poppet valve of the brake booster. The poppet valve engages both the valve piston assembly and a control housing assembly connected to the diaphragm. The relative positions of the poppet valve, valve piston assembly, and control housing determines various states of the booster, and hence, a plurality of sensors can be replaced with the single sensor of the present invention.